Modular design-double insulated field

ABSTRACT

In a power tool, an electric motor is mounted on an electrically conductive frame by an electrically insulating shield member which directly insulates the motor from the frame and also shields the motor field magnets against spark-gap conduction of electricity to the frame, preventing possible shock to the user.

Unitedv States Patent Jacyno [4 1 May 23, 1972 [54] MODULARDESIGN-DOUBLE 3,344,291 9/1967 Pratt ..310/50 INSULATED FIELD 3,432,7033/1969 Sheps et a1.. ..310/50 3,440,465 4/1969 Pratt et a1. ....310/50 X[721 Invent Jacym, Aurora, 3,462,623 8/1969 Batson et a1. .....310/50[73] Assignee: G. W. Murphy Industries, Inc., Houston, 3,476,960 11/1969Rees ..310/50 3,518,465 6/1970 Jepson et a1. ..310/50 X [22] Filed: May15, 1970 Primary Examiner-L. T. HiX

Assistant Examiner-Mark O. Budd [211 App]' 37310 Attorney-Hofgren,Wegner, Allen, Ste1lman&McCord [52] US. Cl..... ..310/47, 310/50 [57]ABSTRACT [51] "Hozk 7/14 In a power tool an electric motor is mounted onan electri- [58] Field 0! Search ..310/47,50 Cally conductive frame y anelectrically insulating shield member which directly insulates the motorfrom the frame [56] References Cited and also shields the motor fieldmagnets against spark-gap UNTTED STATES PATENTS conduction ofelectricity to the frame, preventing possible shock to the user.3,119,942 l/1964 Luther....' ..310/50 X 3,283,185 11/1966 Somers et a1...310/47 7 Claims, 6 Drawing Figures MODULAR DESIGN-DOUBLE INSULATEDFIELD BACKGROUND OF THE INVENTION 1. Field of the Invention Thisinvention relates to systems for mounting electric motors in power toolsand more particularly relates to such mounting systems which preventconduction of electricity from the motor to the power tool frame.

2. Brief Description of the Prior Art A variety of systems havepreviously been provided for mounting motors in power tools andespecially in portable or hand tools. Such mounting systems usuallysecure the motor directly to a frame. The frame can be an integral partof the casing or can be a separate member which is secured to thecasing. The casings are often of electrically conductive metal althoughplastic casings are becoming more and more popular. Some casings arepart plastic, e.g., the motor containing portion, and part metal, e.g.,the handle and trigger portion. However, regardless of what type ofmaterial is used, where the frame which mounts the motor is electricallyconductive, there is danger of shock to the user from current conductedfrom the motor to the frame, for example as may occur from a faultyinsulation or a failure in insulation on the wire in the motor fieldwindings during use of the device.

SUMMARY OF THE INVENTION This invention is an improvement in devicesdriven by electric motors, and especially in portable tools such asdrills, saws, hedgers, etc. The present invention is useful in anydevice having a frame made of or containing electrically conductivematerial. It is especially useful in those devices in which the motor ismounted on a motor mounting plate or an assembly of motor mountingplates, although it can be used in devices using other motor mountingsystems which may or may not be integral with the tool casing. Briefly,the invention provides an insulating shield system for mounting themotor on the device frame. The insulating shield serves not only todirectly electrically insulate the motor from the frame, but also servesto block spark jump acrossthe spark gap between the motor and frame. I

While this invention is susceptible of embodiment in many differentforms, there is shown in the drawing and will hereafter be described indetail a form of the invention with the understanding that the presentdisclosure is to be considered as an exemplification of the principlesof the invention and is not intended to limit the invention to the formillustrated.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary plan view ofan assembly of an electric motor and drive system on a motor mountingplate module and embodying a form of the insulating system of thisinvention;

FIG. 2 is an enlarged perspective view of an insulating member of thesystem of the device of FIG. 1 showing two portions thereof explodedfrom each other; 8

FIG. 3 is an enlarged section along line 3-3 in FIG. 1;

FIG. 4 is a bottom plan view of one portion of the insulating membershown in FIG. 2;

FIG. 5 is a partial cross-sectional view of the insulating members inuse on a motor with a longer field stack; and

FIG. 6 is a view similar to FIG. 5 only showing a still larger motorfield stack.

' DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings andparticularly the assembly of FIG. 1, there is shown a motor mountingframe 10 which includes two plates 12 and 14 stamped in a singleoperation from a blank of electrically conductive sheet metal asdescribed in the copending application of Anthony Jacyno, entitled SheetMetal Frame Module," Ser. No. 850,834, filed Aug. 18, I969. Thedisclosure of said application Ser. No. 850,834 is hereby incorporatedby reference.

Plates 12 and 14 are secured face to face by suitable bolts, rivets,spot welds, or like means as at 16. The plates 12 and 14 may be mirrorimages of one another so that when placed in contiguous relation andfastened together the various recesses 18 and openings 20 in the plateswill be aligned with one another to provide support for a motor assemblyshown generally at 22 and a gear train assembly shown generally at 24.The recesses 18 are mostly semi-spherical struck portions formed duringstamping of the plates 12 and 14 and the openings 20 are likewise formedduring the stamping operation.

In general, the motor and drive train assemblies are mounted between theframe plates 12 and 14 by bearings received within bearing receiversformed by the recesses 18. The openings 20 accommodate the motorassembly 22 and gear train assembly 24 such as to permit free movementof all moving parts. The gear train assembly 24 drives a shaft 26 whichhas a tool such as a chuck 28 mounted thereon for rotation therewith.

The motor assembly 22 has a rotor portion including a wound armature 32on a shaft 34 which is in turn received by mounting bearings adjacentopposing ends of shaft 34 for free rotation of the rotor portion. Thestator 30 of the electric motor assembly 22 includes the field magnetsof the motor. The stator 30 has a pair of mounting bores 40 and 42extending longitudinally into a stack of plates of magnetizable ironforming the core on which the field windings (not shown) are wound. Thebores 40 and 42 are spaced approximately from each other around the axisof shaft 34 and have their axes radially spaced from the axis of shaft34. The bores 40 and 42 are axially spaced from pairs of inward facingbore-like or tubular receivers 44, 46 and 48, 50 between the frameplates 12 and 14. Receivers 44 and 46 are axially aligned with eachother and with bore 40 while receivers 48 and 50 are axially alignedwith each other and with bore 42.

It will be noted in FIG. 1 that opening 20 is shaped to leave a spacebetween stator 30 and the mounting frame 10 including a gap adjacenteach pair of receivers 44, 46 and 48, 50. Each of the gaps is filledwith a mounting member 52 or 54 which serves to secure the rotor 30against movement relative to the plate frame 10. As best seen in FIGS. 2through 4, each mounting member 52 or 54 includes two portions 56 and 58each having a thick cylindrical section or shielding element 60 much inthe form of a longitudinal section of a cylindrical wall of a hollowtube. Mounting portion 56 has an inwardly stepped outer surface at 62and mounting portion 58 has an outwardly stepped inner surface at 64such that when the mounting portions 56 and 58 are slid axially towardeach other from the position of FIG. 2 to that of FIG. 1, they mate andthe shield element 60 is formed as a contiguous element with a steppedjoint shown at 70.

Each of mounting member portions 56 and 58 has an inwardly extendingintegral arm 66 at the end of shield element 60. Each arm 66 has anintegral pin 68 which has an inwardly projecting pin element 68a and anoutwardly projecting pin element 68b.

To assemble the device as shown in FIG. 1, the pin elements 68a ofmounting members 52 and 54 are axially slid into the ends of bores 40and 42 of stator 30 until properly joined at 70. The motor and geartrain assemblies are then laid out on plate 14 with bearings received inappropriate recesses 18 and with pin elements 68b received inappropriate semi-cylindrical recesses which form halves of recesses 44,46, 48 and 50. Plate 12 is then placed over the assembly in mirror imagefashion to complete the recesses 18 which hold the bearings and tocomplete recesses 44, 46, 48 and 50 which hold pins 68b. The two plates12 and 14 are then secured face-to-face to each other. The resultingplate frame 10 is then mounted in a suitable casing of electricallyconducting metal or electrically nonconducting plastic or a combinationof both.

The motor armature windings are supplied with electric current throughbrushes 72 which are received in suitable insulating receivers 74 whichare in turn secured by suitable means to the plate frame 10. If duringoperation of the device electric dinal length are provided withborescurrent should be transmitted into the field magnet core of stator 30,e.g., by initial faulty insulation or development of faulty insulationin the field windings or even in armature windings 32 during operation,the electrical current will not be transmitted directly to the plateframe 10 because mounting members 52 and 54 are of electricallyinsulating material which block such transmission. Additionally, eachshield portion 60 of electrically insulating mounting members 52 and 54extends a sufficient distance to both sides of the plate frame 10 toblock spark jump across the gap between the magnet core of stator 30 andplate frame 10.

FIGS. 5 and 6 illustrate that the mounting members can be adjusted foruse on various size stator or field stack structures. Only one mountingmember 152 is shown, but it is understood that two are intended asdescribed with respect to FIG. 1. Specifically, field stacks or stators130 of different longitu- 140 for receiving the inwardly projecting pinelements 168a and 168b on the mounting portions 156 of mounting member152. As can be seen, the stator 130 of FIG. 5 is longer than the stator30 of FIG. 1 while in FIG. 6 the stator is longer yet. in both cases ofFIGS. 5 and 6 the effect is to s read the overlapping stepped surfaces162 and 164 but to still maintain a complete insulating barrier orshield between the stator and the metal frame or housing. Within thelimits provided by the longitudinal lengths of overlapping steppedsurfaces 162 and 164 motors of various longitudinally sized stators areusable with my invention for insulating motors from metal frames ormountings.

lclaim:

l. A power tool including an electric motor having a stator member,electrically conductive frame means, insulating shield means positionedbetween said frame means and the stator of said motor, and mountingmeans carried by said shield means for securing said motor on saidframe, said insulating shield means shielding against spark jump fromthe motor to the frame means, said insulating shield means comprising alongitudinal tube section shell of insulating material with integralradially inwardly depending arm members, inwardly and outwardlyprojecting opposing integral pins in axial alignment extending fromopposing sides of each arm member on an axis parallel with the axis ofsaid tube section with all of said pins on the same approximate axis, abore in the stator of said motor parallel to and spaced from the axis ofthe motor shaft and receivingthe inwardly projecting pins of saidinsulating shield means and receiver means in said frame receiving theoutwardly projecting pins of said insulating shield means.

2. The device of claim 1 wherein said frame means comprises first andsecond stamped sheet metal members of generally planar configurationwhich are at least in part mirror images of one another and whichinclude means receiving said mounting means between said stamped sheetmembers for holding said shield means relative to said frame means.

3. A power too] including an electric motor having a stator member,electrically conductive frame means, insulating shield means positionedbetween said frame means and the stator of said motor, and mountingmeans carried by said shield means for securing said motor on saidframe, said insulating shield means shielding against spark jump fromthe motor to the frame means, said insulating shield means comprising apair of shield portions having cooperating joint surfaces for slidablyjoining said shield portions to provide the shield means, each shieldportion including pin means projecting in the direction of joiningmovement of said shield portions and received by axially slidingmovement in pin receivers in said motor during joining movement of saidshield portions to form the shield, and including means for locking saidshield means to said frame, the frame including abutment means receivingthe shield member and locking said shield portion against separationfrom each other.

4. The device of claim 3 wherein said joint surfaces are cooperatingstepped surfaces.

5. The device of claim 3 wherein said shield means has cylindrical innerand outer surfaces.

. A power tool including an electric motor having a stator member,electrically conductive frame means, insulating shield means positionedbetween said frame means and the stator of said motor, and mountingmeans carried by said shield means for securing said motor on saidframe, said insulating shield means shielding against spark jump fromthe motor to the frame means, said shield means comprising two engaged,partially overlapping members longitudinally slidable to accommodatemotor stators of different longitudinal lengths, said mounting meansbeing formed of insulating material and integral with said shield means.

7. A power tool including an electric motor having a stator member,electrically conductive frame means, insulating shield means positionedbetween said frame means and the stator of said motor, and mountingmeans carried by said shield means for securing said motor on saidframe, said insulating shield means shielding against spark jump fromthe motor to the frame means and being comprised of two engaged,partially overlapping members longitudinally slidable with respect toeach other, said mounting means being integral with said overlappingmembers and comprising insulating pin means located radially inwardly ofthe outermost peripheral extent of said overlapping members.

1. A power tool including an electric motor having a stator member,electrically conductive frame means, insulating shield means positionedbetween said frame means and the stator of said motor, and mountingmeans carried by said shield means for securing said motor on saidframe, said insulating shield means shielding against spark jump fromthe motor to the frame means, said insulating shield means comprising alongitudinal tube section shell of insulating material with integralradially inwardly depending arm members, inwardly and outwardlyprojecting opposing integral pins in axial alignment extending fromopposing sides of each arm member on an axis parallel with the axis ofsaid tube section with all of said pins on the same approximate axis, abore in the stator of said motor parallel to and spaced from the axis ofthe motor shaft and receiving the inwardly projecting pins of saidinsulating shield means and receiver means in said frame receiving theoutwardly projecting pins of said insulating shield means.
 2. The deviceof claim 1 wherein said frame means comprises first and second stampedsheet metal members of generally planar configuration which are at leastin part mirror images of one another and which include means rEceivingsaid mounting means between said stamped sheet members for holding saidshield means relative to said frame means.
 3. A power tool including anelectric motor having a stator member, electrically conductive framemeans, insulating shield means positioned between said frame means andthe stator of said motor, and mounting means carried by said shieldmeans for securing said motor on said frame, said insulating shieldmeans shielding against spark jump from the motor to the frame means,said insulating shield means comprising a pair of shield portions havingcooperating joint surfaces for slidably joining said shield portions toprovide the shield means, each shield portion including pin meansprojecting in the direction of joining movement of said shield portionsand received by axially sliding movement in pin receivers in said motorduring joining movement of said shield portions to form the shield, andincluding means for locking said shield means to said frame, the frameincluding abutment means receiving the shield member and locking saidshield portion against separation from each other.
 4. The device ofclaim 3 wherein said joint surfaces are cooperating stepped surfaces. 5.The device of claim 3 wherein said shield means has cylindrical innerand outer surfaces.
 6. A power tool including an electric motor having astator member, electrically conductive frame means, insulating shieldmeans positioned between said frame means and the stator of said motor,and mounting means carried by said shield means for securing said motoron said frame, said insulating shield means shielding against spark jumpfrom the motor to the frame means, said shield means comprising twoengaged, partially overlapping members longitudinally slidable toaccommodate motor stators of different longitudinal lengths, saidmounting means being formed of insulating material and integral withsaid shield means.
 7. A power tool including an electric motor having astator member, electrically conductive frame means, insulating shieldmeans positioned between said frame means and the stator of said motor,and mounting means carried by said shield means for securing said motoron said frame, said insulating shield means shielding against spark jumpfrom the motor to the frame means and being comprised of two engaged,partially overlapping members longitudinally slidable with respect toeach other, said mounting means being integral with said overlappingmembers and comprising insulating pin means located radially inwardly ofthe outermost peripheral extent of said overlapping members.